Most everyone in our region knows that the Red River forms a border between North Dakota and Minnesota. However, it might surprise you that the Red River does not delineate the entire eastern border.
Many people may have forgotten that the Red River of the North begins with the confluence of the Bois de Sioux and Otter Tail rivers in Wahpeton-Breckenridge. From there, “The Red” meanders northward through Fargo-Moorhead and Grand Forks-East Grand Forks before crossing into Manitoba near Pembina. But that leaves the state line southward from Wahpeton-Breckenridge to the South Dakota state line undetermined.
It is the Bois de Sioux River that serves as the border between North Dakota and Minnesota southward of the confluence of the two rivers at Wahpeton-Breckenridge.
No doubt many of you are familiar with Lake Traverse, a lake of around 11,000 acres which lies on that little wedge of Minnesota that looks to be pushing into northeast South Dakota. The outlet at the upper end of the lake is the Bois de Sioux River. It initially flows in a northeasterly direction forming the boundary between South Dakota and Minnesota and through a smaller lake (Mud Lake) before bending to a more northerly route on its way Wahpeton-Breckenridge.
The Otter Tail River, on the other hand, begins in Becker County, Minnesota southwest of Bemidji. It then flows for around 200 miles through communities including Frazee, Ottertail, and Fergus Falls before merging with the Bois de Sioux River in Wahpeton-Breckenridge.
I recently ran across an article by John Bluemle, former state geologist and director of the North Dakota Geological Survey, about the determination of North Dakota’s borders. He notes that North Dakota has no law designating the North Dakota-Minnesota border south of the confluence of the Boise de Sioux and Otter Tail rivers. The state of Minnesota, however, has — so that portion of the border with Minnesota is, by default, determined by Minnesota law.
